Sensor and method for remote detection of objects

Abstract

A sensor for remote detection of objects ( 20 ), preferably for use in an article surveillance system, comprises a wireshaped element ( 22 ), which is arranged to be excited and detected electromagnetically. The wireshaped element ( 22 ) has a diameter less than 30 μm. The element is arranged to transmit an electromagnetic reply signal, the amplitude of which is modulated in response to an externally applied and time-varying magnetic field. According to a method of detecting the presence of an object ( 20 ) in a surveillance zone ( 10 ), the object is provided with at least one wireshaped element ( 22 ) of amorphous or nanocrystalline metal alloy with magnetic properties and with a diameter less than 30 μm. Electromagnetical signals are generated in the surveillance zone for exciting the wireshaped element. Furthermore, a time-varying magnetic modulating field is generated in the surveillance zone. Electromagnetic signals generated by the wireshaped element are received and analyzed with respect to a modulation in amplitude caused by the magnetic modulating field, so as to determine the presence of the element (and consequently the object) in the surveillance zone.

What is claimed is:  
     
       1. A sensor for remote detection of objects, preferably for use in an article surveillance system, comprising: 
       a wire_shaped element arranged to be excited and detected electromagnetically,  
       wherein the wire_shaped element has a diameter less than 30 μm, and  
       the element is arranged to transmit an electromagnetic reply signal, the amplitude of the reply signal being modulated in response to an externally applied time-varying magnetic field.  
     
     
       2. A sensor according to claim  1 , wherein the wire_shaped element comprises an amorphous metal alloy. 
     
     
       3. A sensor according to claim  1 , wherein the wire_shaped element comprises a nanocrystalline metal alloy. 
     
     
       4. A sensor according to any one of claims  2  or  3 , wherein the metal alloy is cobalt-rich. 
     
     
       5. A sensor according to any one of claims  1 - 3 , wherein the permeability of the metal alloy is controllable through the varying magnetic field. 
     
     
       6. A sensor according to any one of claims  1 - 3 , wherein the wire_shaped element is covered with a coating of glass or other dielectrical material. 
     
     
       7. A sensor according to any one of claims  1 - 3 , wherein the wire_shaped element has an essentially circular cross-section and is straight in a longitudinal direction of the element. 
     
     
       8. A sensor according to any one of claims  1 - 3 , wherein the wire_shaped element extends helically or helicoidally in a longitudinal direction. 
     
     
       9. A sensor according to any one of claims  1 - 3 , including a wire_shaped support element of non-magnetic material, the support element being twisted together with said wire_shaped elmenet of magnetic material. 
     
     
       10. A method of detecting the presence of an object in a surveillance zone, comprising the steps of: 
       providing the object with at least one wire_shaped element of amorphous or nanocrystalline metal alloy with magnetic properties and with a diameter less than 30 μm,  
       generating electromagnetic signals in the surveillance zone for exciting the wire_shaped element,  
       generating a time-varying magnetic modulating field in the surveillance zone,  
       receiving electromagnetic signals generated by the wire_shaped element, and  
       analyzing the received electromagnetic signals with respect to a modulation in amplitude caused by the magnetic modulating field, so as to determine the presence of the element—and consequently the object—in the surveillance zone.  
     
     
       11. A method according to claim  10 , wherein said object is an article of clothing and the wire_shaped element is provided in a label located in the article of clothing. 
     
     
       12. A method according to claim  10 , wherein said object is an article of clothing and said wire_shaped element is sewn into a collar in the article of clothing. 
     
     
       13. A method according to claim  10 , wherein said object is an article of clothing, and the wire_shaped element is woven into a cloth, from which the article of clothing is manufactured. 
     
     
       14. A method according to claim  10 , wherein said object is packed in cardboard, paper or similar material and the wire_shaped element is integrated in the packing material at the manufacturing thereof. 
     
     
       15. A method according to claim  10 , wherein said object is packed in a plastic film or similar material, and the wire_shaped element is integrated in the plastic film at the manufacturing thereof.